1. Field of the Invention
The present invention relates generally to an electrical capacitor formed of a consolidated stack of dielectric layers, each layer having a metal antipolar coating, and further to a method for the manufacture of such capacitor.
An electrical capacitor is disclosed in U.S. Pat. No. 4,563,724 that is formed of a consolidated stack of dielectric layers laminated to one another, each dielectric layer being provided with a metal coating layer. The metal coatings on alternate layers extend to alternate ones of two projections. The projections are formed in the consolidated stack by an incision roughly in the center of one side of the stack and proceeding in the direction of the thickness of the stack. The end surfaces of the projections are provided with metal contact layers which contact and connect the metal coatings to one another to form anti-polar coatings of the electrical capacitor.
Additional features of the disclosed capacitor include:
(a) the dielectric layers are composed of plastic films;
(b) the coatings are composed of regenerably thin layers of valve metal. Each coating covers a respective surface of a dielectric layer practically up to the edges at the long sides of the consolidated stack, as well as up to both ends of the projections. In some embodiments, the metal coatings extend up to the edge of an upper narrow side of the stack which lies opposite the stack side containing the incision;
(c) alternating from dielectric layer to dielectric layer, the projections are provided with metal-free insulating strips which form remaining metal strips at the ends of the projections. The incision is at least greater than the width of the remaining metal strips, and preferably coincides with or extends beyond the inner edges of the insulating strips;
(d) the metal contacts connecting the antipolar coatings to one another are produced by metal spraying;
(e) at least one capacitively ineffective cover layer is provided at a front side and/or a back side of the stack.
A method is also disclosed in the U.S. Pat. No. 4,563,724 for manufacturing the disclosed electrical capacitors. The method includes stacking, or winding, on a drum bands of plastic which are metallized on one side so that a master capacitor is formed. The bands include a wavy cut at one edge side. The resulting master capacitor is divided perpendicularly to the layer planes into individual capacitors.
The disclosed method also includes arranging capacitively ineffective intermediate layers on a plurality of dielectric layers having metal coatings to form a parent capacitor and further arranging capacitively effective dielectric layers with metal coatings thereover for a next parent capacitor. The master capacitor is thereby formed of a plurality of parent capacitors, and is subsequently provided with end contact layers. The master capacitor is divided in the region of the intermediate layers and in a direction perpendicular thereto. The method steps include the following:
(a) two metallized bands are wound onto a drum, each band having a metal-free strip at one edge and intermittent metal-free insulating strips in the region of an opposite edge and spaced therefrom. The intermittent metal-free strips are produced in the winding direction before or during winding such that, as the bands are wound onto the drum, the insulating strips lie in a plane perpendicular to the winding axis, corresponding to the drum shaft. Each end of the intermittent insulating strips extend into or slightly beyond a region into which an incision is later made;
(b) during winding, the bands are conducted onto the drum such that the centers of the intermittent insulating strips of an upper one of the bands are symmetrically arranged above the centers of the spaces between the intermittent insulating strips of a lower one of the bands to generate a parent capacitor;
(c) after winding and consolidation of the master capacitor, or respectively, a parent capacitor, at least one end face formed by the edges of the bands is provided with a metal layer by metal spraying while still on the drum;
(d) after division into individual parent capacitors, incisions are generated perpendicular to the winding direction centrally between two respective cut lines so that two projections are formed as a result of the width and depth of the incisions;
(e) severing the individual capacitors--after, depending upon the embodiment, fastening the power leads--by sawing along the cut lines which proceed through the centers of the intermittent insulating strips; and
(f) finishing the individual capacitors by applying power leads, such as cap-shaped power leads, insofar as power leads have not already been secured in step e).
Another method for manufacturing the electrical capacitors provides that bands of plastic which are metallized at one side are stacked on a drum as dielectric layers to form a master capacitor, the bands having a wavy cut at one edge. The master capacitor is divided into the desired individual capacitors perpendicular to the layer planes and capacitively ineffective intermediate layers are arranged over a plurality of the dielectric layers having coatings to form a parent capacitor. The next parent capacitor is formed by arranging capacitively effective dielectric layers having coatings over the capacitively ineffective intermediate layers. An original capacitor is thereby formed and is provided with end contact layers and subsequently divided in the region of the intermediate layers and in a direction perpendicular thereto. The disclosed method includes the following steps:
(a) metallized bands are wound onto a drum. The metallized bands are provided with intermittent metal-free insulating strips in the winding direction in the region of and spaced from both band edges. The intermittent metal-free strips are provided either before or during winding such that, when the bands are wound onto the drum, the insulating strips are wound in a plane perpendicular to the winding axis. Each end of the intermittent strips extend into or goes slightly beyond a region in which an incision is subsequently formed;
(b) during winding onto the drum, the bands are conducted such that the centers of the insulating strips of an upper band are symmetrically arranged over the centers of the spaces between the insulating strips of a lower band in the finished parent capacitor;
(c) after winding and consolidation of the master capacitor, or respectively, parent capacitor, applying metal layers to both end faces formed by the edges by metal spraying while still on the drum;
(d) after separation into individual parent capacitors, generating incisions at both sides perpendicular to the winding direction in the center between two respective cut lines so that two projections are formed by the width and depth of the incisions;
(e) severing the individual capacitors, possibly after fastening power leads thereto, by sawing along cut lines which proceed through the centers of the intermittent insulating strips, as well as sawing along a cut line which lies in the center of the parent capacitor parallel to the edges; and
(f) finishing the capacitors by applying power leads, such as cap-shaped power leads, insofar as power leads have not been already applied in method step (e).
The disclosed capacitors contain capacitively ineffective cover layers as insulation above the first dielectric layer and below the last dielectric layer. The cover layers are applied in the manufacturing operation in the form of plastic films without metal coatings, so that the cover layers of the finished capacitor do not have metal coatings. See German Pat. No. 1,764,541, corresponding to U.S. Pat. Nos. 3,670,378 and 3,728,765.
German Pat. No. 25 41 111 discloses a method for manufacturing electrical capacitors formed of stacks. According to this method, a plurality of parent capacitors separated from one another by capacitively ineffective intermediate layers are wound onto a large-diameter drum. One or more capacitor foils having successive metal layers to form the two antipolar coatings are wound laterally offset relative to one another so that they alternately extend up to one of the two end faces of the winding and are thus spaced from the other end face of the winding. A parting band which projects beyond the end faces of the capacitor at both sides is wound threaded in the middle of the intermediate layers. A master capacitor which is thus formed has metal contacts applied over both full end faces by the schoopage method. The capacitor is then tempered for mechanical solidification and parted, or separated, in at least one plane which proceeds through the rotational axis of the winding. The parent capacitors, or subsections of parent capacitors, which are formed are parted along the parting band and then divided into individual capacitors by further cuts perpendicular to the running direction of the foil band.
In the region of the intermediate layers the capacitor foils are provided with metal-free longitudinal strips in the metal layers so that the individual capacitors have no capacitively effective coverages in the region of the intermediate layers after a parent winding has been parted. The metal-free longitudinal strips are generated, for example, by electrical discharge machining, erosion by radio frequency or pulses which are supplied by rolling wheels or dragging metal tapes, or are generated by mechanical abrasion such as rotating abrasive wheels. The metal-free strips are preferably generated as close as possible to the winding machine such as, for example, on a deflection roller close to the winding drum if producing the metal-free strips directly on the drum is not possible.
The method provides plastic bands with metal coatings on one side, wherein the metal coatings from plastic band to plastic band alternatingly extend up to opposite ones of the edges. A metal-free strip is provided at the other opposite edge of each plastic band as a result of the metal coating being spaced from the edge. The metal-free longitudinal strip is additionally generated in the proximity of that edge up to which the metal layer extends so that when the end faces of the master capacitor are later connected, the metal coating layer along which the longitudinal strip extends is not connected to the metallized end face. Thus, this plastic layer acts as a cover layer.
The electrical layer capacitor which is the subject of the above-cited U.S. Pat. No. 4,563,724 is constructed, based on the overall structure and manufacturing method, in a completely different way from capacitors resulting from the method of German Pat. No. 25 41 111.
The U.S. Pat. No. 4,563,724 also discloses that the manufacture of intermittent metal-free insulating strips on the metallized tapes can be undertaken through the use of laser beams. Pulses of the laser beam are controlled so that they are synchronized with the rotation of the drum to achieve the desired position and length of the insulating strips relative to one another and also relative to the build up of the parent capacitor as its radius increases.
German Patent Application No. P35 14 824 discloses a particular embodiment for the manufacture of metal-free strips by a laser.